Biodegradable PHA copolymers

ABSTRACT

The present invention relates to biodegradable PHA copolymers comprising at least two randomly repeating monomer units. The present invention further relates to a plastic article comprising a biodegradable copolymer, wherein the biodegradable copolymer comprises at least two randomly repeating monomer units (RRMU) wherein the first RRMU has the structure ##STR1## wherein R 1  is H, or C 1  or C 2  alkyl, and n is 1 or 2; the second RRMU has the structure ##STR2## and wherein at least 50% of the RRMUs have the structure of the first RRMU. The present invention further relates to an absorbent article comprising a liquid pervious topsheet, a liquid impervious backsheet comprising a film comprising a PHA of the present invention and an absorbent core positioned between the topsheet and the backsheet.

TECHNICAL FIELD

The present invention relates to biodegradable PHA copolymers andplastic articles comprising such biodegradable PHA copolymers.

BACKGROUND

Polymers find uses in a variety of plastic articles including films,sheets, fibers, foams, molded articles, adhesives and many otherspecialty products. For applications in the areas of packaging,agriculture, household goods and personal care products, polymersusually have a short (less than 12 months) use cycle. For example, infood packaging, polymers play the role of a protective agent and arequickly disposed of after the contents are consumed. Household productssuch as detergent bottles and diapers are immediately discarded once theproduct is used.

The majority of this plastic material ends up in the solid waste stream,headed for rapidly vanishing and increasingly expensive landfill space.While some efforts at recycling have been made, the nature of polymersand the way they are produced and converted to products limits thenumber of possible recycling applications. Repeated processing of evenpure polymers results in degradation of material and consequently poormechanical properties. Different grades of chemically similar plastics(e.g., polyethylenes of different molecular weights, as used in milkjugs and grocery sacks) mixed upon collection can cause processingproblems that make the reclaimed material inferior or unusable.

Absorbent article applications such as diapers, sanitary napkins,pantiliners and the like, involve several different types of plastics.In these cases, recycling is particularly costly because of thedifficulty in separating the different components. Disposable productsof this type generally comprise some sort of fluid-permeable topsheetmaterial, an absorbent core, and a fluid-impermeable backsheet material.Heretofore, such absorbent structures have been prepared using, forexample, topsheet materials prepared from woven, non-woven, or porousformed-film polyethylene or polypropylene materials. Backsheet materialstypically comprise flexible polyethylene sheets. Absorbent corematerials typically comprise wood pulp fibers or wood pulp fibers incombination with absorbent gelling materials. Although such productslargely comprise materials which would be expected ultimately todegrade, and although products of this type contribute only a very smallpercentage of the total solid waste materials generated by consumerseach year, nevertheless, there is currently a perceived need to devisesuch disposable products from materials which are compostable.

A conventional disposable absorbent product is already to a large extentcompostable. A typical disposable diaper, for example, consists of about80% of compostable materials, e.g., wood pulp fibers, and the like. Inthe composting process soiled disposable absorbent articles are shreddedand commingled with organic waste prior to the composting per se. Aftercomposting is complete, the non-compostable particles are screened out.In this manner even today's absorbent articles can successfully beprocessed in commercial composting plants.

Nevertheless, there is a need for reducing the amount of non-compostablematerials in disposable absorbent articles. There is a particular needto replace polyethylene backsheets in absorbent articles with liquidimpervious films of compostable material, because the backsheet istypically one of the largest non-compostable components of aconventional disposable absorbent article.

In addition to being compostable, the films employed as backsheets forabsorbent articles must satisfy many other performance requirements. Forexample, the resins should be thermoplastic such that conventional filmprocessing methods can be employed. These methods include cast film andblown film extrusion of single layer structures and cast or blown filmcoextrusion of multilayer structures. Other methods include extrusioncoating of one material on one or both sides of a compostable substratesuch as another film, a non-woven fabric, or a paper web.

Still other properties are essential in product converting operationswhere the films are used to fabricate absorbent articles. Propertiessuch as tensile strength, tensile modulus, tear strength, and thermalsoftening point determine to a large extent how well a film will run onconverting lines.

In addition to the aforementioned properties, still other properties areneeded to meet the end user requirements of the absorbent article. Filmproperties such as impact strength, puncture strength, and moisturetransmission are important since they influence the absorbent article'sdurability and containment while being worn.

Once the absorbent article is disposed of and enters a compostingprocess, other properties become important. Regardless of whetherincoming waste is preshredded or not, it is important that the film orlarge film fragments undergo an initial breakup to much smallerparticles during the initial stages of composting. Otherwise, the filmsor large fragments may be screened out of the compost stream and maynever become part of the final compost.

In the past, the biodegradability and physical properties of a varietyof polyhydroxyalkanoates (PHAs) have been studied. Polyhydroxyalkanoatesare polyester compounds produced by a variety of microorganisms, such asbacteria and algae. While polyhydroxyalkanoates have been of generalinterest because of their biodegradable nature, their actual use as aplastic material has been hampered by their thermal instability. Forexample, poly-3-hydroxybutyrate (PHB) is a natural energy-storageproduct of bacteria and algae, and is present in discrete granuleswithin the cell cytoplasm. However, unlike other biologicallysynthesized polymers such as proteins and polysaccharides, PHB isthermoplastic having a high degree of crystallinity and a well-definedmelt temperature of about 180° C. Unfortunately, PHB becomes unstableand degrades at elevated temperatures near its melt temperature. Due tothis thermal instability, commercial applications of PHB have beenextremely limited.

As a result, investigators have studied other polyhydroxyalkanoates suchas poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), in the hopes ofdiscovering a polyhydroxyalkanoate having sufficient thermal stabilityand other suitable chemical and physical properties for use in practicalapplications. Unfortunately, polyhydroxyalkanoates such as PHB and PHBVare difficult to process into films suitable for backsheet applications.As previously discussed, the thermal instability of PHB makes suchprocessing nearly impossible. Furthermore, the slow crystallizationrates and flow properties of PHB and PHBV make film processingdifficult. Examples of PHB homopolymer and PHBV copolymers are describedin U.S. Pat. No. 4,393,167, Holmes et al., issued Jul. 12, 1983, andU.S. Pat. No. 4,880,592, issued Nov. 14, 1989. PHBV copolymers arecommercially available from Imperial Chemical Industries under thetradename BIOPOL. PHBV copolymers are currently produced with valeratecontents ranging from about 5 to about 24 mol %. Increasing valeratecontent decreases the melt temperature, crystallinity, and stiffness ofthe polymer. An overview of BIOPOL technology is provided in BUSINESS2000+ (Winter, 1990).

Due to the slow crystallization rate, a film made from PHBV will stickto itself even after cooling; a substantial fraction of the PHBV remainsamorphous and tacky for long periods of time. In cast film operations,where the film is immediately cooled on chill rolls after leaving thefilm die, molten PHBV often sticks to the rolls restricting the speed atwhich the film can be processed, or even preventing the film from beingcollected. In blown films, residual tack of the PHBV causes the tubularfilm to stick to itself after it has been cooled and collapsed forwinding.

U.S. Pat. No. 4,880,592, Martini et al., issued Nov. 14, 1989, disclosesa means of achieving a PHBV monolayer film for diaper backsheetapplications by coextruding the PHBV between two layers of sacrificialpolymer, for example a polyolefin, stretching and orienting themultilayer film, and then stripping away the polyolefin layers after thePHBV has had time to crystallize. The remaining PHBV film is thenlaminated to either water soluble films or water insoluble films such aspolyvinylidene chloride or other polyolefins. Unfortunately, suchdrastic and cumbersome processing measures are necessary in an attemptto avoid the inherent difficulties associated with processing PHBV intofilms.

Based on the foregoing, there is a need for plastic articles that canbiodegrade. In effect such biodegradable articles would facilitate the"recycling" of plastic articles into another usable product, topsoil,through composting. To satisfy this need, there is a preliminary needfor a biodegradable polymer which is capable of being easily processedinto a plastic article for use in a disposable product.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a biodegradablepolyhydroxyalkanoate (PHA) copolymer.

It is also an object of the present invention to provide plasticarticles comprising a biodegradable polyhydroxyalkanoate (PHA).

It is also an object of the present invention to provide a method ofusing a biodegradable polyhydroxyalkanoate (PHA) to make plasticarticles.

It is also an object of the present invention to provide a disposablesanitary garment comprising a film comprising a biodegradablepolyhydroxyalkanoate (PHA).

SUMMARY

The present invention relates to novel biodegradablepolyhydroxyalkanoate (PHA) copolymers comprising at least two randomlyrepeating monomer units.

The present invention further relates to plastic articles comprising abiodegradable copolymer, wherein the copolymer comprises at least tworandomly repeating monomer units wherein the first monomer unit has thestructure ##STR3## wherein R¹ is H, or C₁ or C₂ alkyl, and n is 1 or 2;the second monomer unit has the structure ##STR4## and wherein at least50% of the random repeating monomer units have the structure of thefirst monomer unit. Such plastic articles include films, sheets, fibers,foams, molded articles, nonwoven fabrics, elastomers, and adhesives.

The present invention further relates to an absorbent article comprisinga liquid pervious topsheet, a biodegradable liquid impervious backsheetcomprising a film comprising a biodegradable PHA, and an absorbent corepositioned between the topsheet and the backsheet.

DETAILED DESCRIPTION

The present invention answers the need for a biodegradable copolymerwhich is capable of being easily processed into a plastic article. Thepresent invention further answers the need for disposable plasticarticles with increased biodegradability and/or compostability.

As used herein, "ASTM" means American Society for Testing and Materials.

As used herein, "comprising" means that other steps and otheringredients which do not affect the end result can be added. This termencompasses the terms "consisting of" and "consisting essentially of".

As used herein, "alkyl" means a saturated carbon-containing chain whichmay be straight or branched; and substituted (mono- or poly-) orunsubstituted.

As used herein, "alkenyl" means a carbon-containing chain which may bemonounsaturated (i.e., one double bond in the chain) or polyunsaturated(i.e., two or more double bonds in the chain); straight or branched; andsubstituted (mono- or poly-) or unsubstituted.

As used herein, "PHA" means a polyhydroxyalkanoate of the presentinvention.

As used herein, "PHB" means the homopolymer poly-(3-hydroxybutyrate).

As used herein, "PHBV" means the copolymerpoly(3-hydroxybutyrate-co-3-hydroxyvalerate).

As used herein, "PHBMV" means the copolymerpoly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate).

As used herein, "biodegradable" means the ability of a compound toultimately be degraded completely into CO₂ and water or biomass bymicroorganisms and/or natural environmental factors.

As used herein, "compostable" means a material that meets the followingthree requirements: (1) the material is capable of being processed in acomposting facility for solid waste; (2) if so processed, the materialwill end up in the final compost; and (3) if the compost is used in thesoil, the material will ultimately biodegrade in the soil.

For example, a polymer film material present in solid waste submitted toa composting facility for processing does not necessarily end up in thefinal compost. Certain composting facilities subject the solid wastestream to air classification prior to further processing, in order toseparate paper and other materials. A polymer film would most probablybe separated from the solid waste stream in such an air classificationand therefore not be processed in the composting facility. Nevertheless,it may still be a "compostable" material according to the abovedefinition because it is "capable" of being processed in a compostingfacility.

The requirement that the material ends up in the final compost typicallymeans that it undergoes a form of degradation in the composting process.Typically, the solid waste stream will be subjected to a shredding stepin an early phase of the composting process. As a result, the polymerfilm will be present as shreds rather than a sheet. In the final phaseof the composting process, the finished compost will be subjected to ascreening step. Typically, the polymer shreds will not pass through thescreens if they have retained the size they had immediately after theshredding step. The compostable materials of the present invention willhave lost enough of their integrity during the composting process toallow partially degraded shreds to pass through the screens. However, itis conceivable that a composting facility might subject the solid wastestream to a very rigorous shredding and a rather coarse screening, inwhich case nondegradable polymers like polyethylene would meetrequirement (2). Therefore, meeting requirement (2) is not enough for amaterial to be compostable within the present definition.

What distinguishes the compostable material as defined herein frommaterial like polyethylene is requirement (3), that the materialultimately biodegrade in the soil. This biodegradability requirement isnot essential to the composting process or the use of composting soil.Solid waste and the compost resulting therefrom may contain all kinds ofnonbiodegradable materials, for example, sand. However, to avoid a buildup of man-made materials in the soil, it is required herein that suchmaterials be fully biodegradable. By the same token, it is not at allnecessary that this biodegradation be fast. As long as the materialitself and intermediate decomposition products are not toxic orotherwise harmful to the soil or crops, it is fully acceptable thattheir biodegradation takes several months or even years, since thisrequirement is present only to avoid an accumulation of man-madematerials in the soil.

All copolymer composition ratios recited herein refer to mole ratios,unless specifically indicated otherwise.

The present invention relates to biodegradable copolymers which aresurprisingly easy to process into plastic articles, particularly intofilms as compared to the homopolymer PHB and copolymer PHBV.

As used herein, "plastic article" means a copolymer processed into afilm, sheet, fiber, foam, molded article, nonwoven fabric, elastomer oradhesive.

PHAs useful for processing into plastic articles of the presentinvention comprise at least two randomly repeating monomer units (RRMU).The first RRMU has the structure ##STR5## wherein R¹ is H, or C₁ or C₂alkyl, and n is 1 or 2. The second RRMU has the structure ##STR6##

In one embodiment of the present invention, at least about 50%, but lessthan 100%, of the RRMUs have the structure of the first RRMU; morepreferably at least about 60%; more preferably at least about 70%; morepreferably at least about 80%; more preferably still at least about 90%.

When a PHA of the present invention is processed into a film, sheet, orsoft elastic fiber, preferably from about 50% to about 99.9% of theRRMUs have the structure of the first RRMU unit; more preferably fromabout 75% to about 99%; more preferably still from about 85% to about98%; most preferably 85% to about 95%.

When a PHA of the present invention is processed into a normal fiber ormolded article (e.g., injected or blown molded) preferably from about80% to about 99.5% of the first RRMUs have the structure of the firstRRMU; more preferably from about 90% to about 99.5%; more preferablystill from about 95% to about 99.5%.

When a PHA of the present invention is processed into an elastomer or anadhesive, preferably from about 50% to 85% of the RRMUs have thestructure of the first RRMU.

When a PHA of the present invention is processed into a nonwoven,preferably from about 85% to about 99.5% of the RRMUs have the structureof the first RRMU; more preferably from about 90% to about 99.5%; morepreferably still from about 95% to about 99.5%.

In one embodiment of the present invention, R¹ is a C₁ alkyl and n is 1,thereby forming the monomeric repeat unit 3-hydroxybutyrate.

In another embodiment of the present invention, R¹ is a C₂ alkyl and nis 1, thereby forming the monomeric repeat unit 3-hydroxyvalerate.

In another embodiment of the present invention, R¹ is H and n is 2,thereby forming the monomeric repeat unit 4-hydroxybutyrate.

In another embodiment of the present invention, R¹ is H and n is 1,thereby forming the monomeric repeat unit 3-hydroxypropionate.

In another embodiment, the copolymer useful in the present inventioncomprises one or more additional RRMUs having the structure ##STR7##wherein R³ is H, or a C₁, C₂, C₃, C₄, C₅, C₆, C₇, C₈, C₉, C₁₀, C₁₁, C₁₂,C₁₃, C₁₄, C₁₅, C₁₆, C₁₇, C₁₈, or C₁₉ alkyl or alkenyl; and m is 1 or 2;and wherein the additional RRMUs are not the same as the first RRMU orthe second RRMU. Preferably the copolymer comprises 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more different RRMUs.

In a preferred embodiment of the present invention, R³ is a C₁, C₂, C₃,C₄, C₅, C₆, C₇, C₈, C₉, C₁₀, C₁₁, C₁₂, C₁₃, C₁₄, C₁₅, C₁₆, C₁₇, C₁₈, orC₁₉ alkyl or alkenyl; and m is 1.

In a preferred embodiment of the present invention, R³ is a C₁ alkyl andm is 1, thereby forming the monomeric repeat unit 3-hydroxybutyrate.

In another embodiment of the present invention, R³ is a C₂ alkyl and mis 1, thereby forming the monomeric repeat unit 3-hydroxyvalerate.

In another embodiment of the present invention, R³ is H and m is 2,thereby forming the monomeric repeat unit 4-hydroxybutyrate.

In another embodiment of the present invention, R³ is H and m is 1,thereby forming the monomeric repeat unit 3-hydroxypropionate.

Preferably, novel biodegradable PHAs of the present invention comprisingtwo RRMUs have a first RRMU having the structure ##STR8## wherein R¹ isH, or C₁ or C₂ alkyl, and n is 1 or 2; and a second RRMU having thestructure ##STR9## wherein at least 50% of the RRMUs have the structureof the first RRMU.

Preferably, novel biodegradable PHAs of the present invention comprisingthree RRMUs, have a first RRMU having the structure ##STR10## wherein R¹is H, or C₁ or C₂ alkyl or alkenyl, and n is 1 or 2; a second RRMUhaving the structure ##STR11## and a third RRMU having the structure##STR12## wherein R³ is H, or a C₁, C₂, C₃, C₄, C₅, C₆, C₇, C₈, C₉, C₁₀,C₁₁, C₁₂, C₁₃, C₁₄, C₁₅, C₁₆, C₁₇, C₁₈, or C₁₉ alkyl or alkenyl; and mis 1 or 2; wherein at least 50% of the RRMUs have the structure of thefirst RRMU; and wherein the third RRMUs is not the same as the firstrandomly repeating monomer unit or the second randomly repeating monomerunit.

Synthesis of Biodegradable PHAs

The biodegradable PHAs of the present invention can be synthesized bysynthetic chemical or biological based methods. A chemical approachinvolves the ring-opening polymerization of β-lactone monomers asdescribed below. The catalysts or initiators used can be a variety ofmaterials such as aluminoxanes, distannoxanes, or alkoxy-zinc andalkoxy-aluminum compounds (see Agostini, D. E., J. B. Lando, and J. R.Shelton, J. POLYM. SCI. PART A-1, Vol. 9, pp. 2775-2787 (1971); Gross,R. A., Y. Zhang, G. Konrad, and R. W. Lenz, MACROMOLECULES, Vol. 21, pp.2657-2668 (1988); and Dubois, P., I. Barakat, R. Jerome, and P. Teyssie,MACROMOLECULES, Vol. 26, pp. 4407-4412 (1993); Le Borgne, A. and N.Spassky, POLYMER, Vol. 30, pp. 2312-2319 (1989); Tanahashi, N., and Y.Doi, MACROMOLECULES, Vol. 24, pp. 5732-5733 (1991); Hori, Y., M. Suzuki,Y. Takahashi, A. Ymaguchi, and T. Nishishita, MACROMOLECULES, Vol. 26,pp. 4388-4390 (1993); and Kemnitzer, J. E., S. P. McCarthy, and R. A.Gross, MACROMOLECULES, Vol. 26, pp. 1221-1229 (1993)). The production ofisotactic polymer can be accomplished by polymerization of anenantiomerically pure monomer and a non-racemizing initiator, witheither retention or inversion of configuration of the stereocenter, orby polymerization of racemic monomer with an initiator whichpreferentially polymerizes one enantiomer. For example: ##STR13##

The naturally derived PHAs of the present invention are isotactic andhave the R absolute configuration at the stereocenters in the polymerbackbone. Alternatively, isotactic polymers may be made where theconfiguration of the stereocenters is predominantly S. Both isotacticmaterials will have the same physical properties and most of the samechemical reactivities except when a stereospecific reagent, such as anenzyme, is involved. Atactic polymers, polymers with randomincorporation of R and S stereocenters, can be produced from racemicmonomers and polymerization initiators or catalysts that show nopreference for either enantiomer while such initiators or catalystsoften polymerize monomers of high optical purity to isotactic polymer(e.g., distannoxane catalysts) (see Hori, Y., M. Suzuki, Y. Takahashi,A. Yamaguchi, T. Nishishita, MACROMOLECULES, Vol. 26, pp. 5533-5534(1993)). Alternatively, isotactic polymer can be produced from racemicmonomers if the polymerization catalyst has an enhanced reactivity forone enantiomer over the other. Depending on the degree of preference,separate R or S stereo-homopolymers, stereo-block copolymers, or amixture of stereo-block copolymers and stereo-homopolymers may beproduced (see Le Borgne, A. and N. Spassky, N., POLYMER, Vol. 30, pp.2312-2319 (1989); Tanahashi, N., and Y. Doi, MACROMOLECULES, Vol. 24,pp. 5732-5733 (1991); and Benvenuti, M. and R. W. Lenz, J. POLYM. SCI.:PART A: POLYM. CHEM., Vol. 29, pp. 793-805 (1991)). Some initiators orcatalysts are known to produce predominantly syndiotactic polymers,polymers with alternating R and S stereocenter repeat units, fromracemic monomers (see Kemnitzer, J. E., S. P. McCarthy and R. A. Gross,MACROMOLECULES, Vol. 26, pp. 1221-1229 (1993)) while some initiators orcatalysts may produce all three types of stereopolymers (see Hocking, P.J. and R. H. Marchessault, POLYM. BULL., Vol. 30, pp. 163-170 (1993)).

For example, preparation ofpoly(3-hydroxybutyrate-co-3-hydroxyalkanoate) copolymers wherein the3-hydroxyalkanoate comonomer is a 3-alkyl-β-propiolactone wherein thealkyl group contains at least three (3) carbons long, are carried out inthe following manner. Proper precautions are made to exclude air andmoisture. The lactone monomers (purified, dried, and stored under inertatmosphere), β-butyrolactone and a 3-alkyl-β-propiolactone in thedesired molar ratio, are charged via syringe or canula to an oven-dried,argon-purged, and flamed borosilicate-glass tube or flask capped with arubber septum. The polymerization catalyst is added as a toluenesolution via syringe. The tube is carefully swirled to mix the reagents(but not contact the rubber septum) and then heated in an oil bath atthe desired temperature for the prescribed time. As the reactionproceeds the mixture becomes viscous and may solidify. If isotacticpolymer is produced, solid polymer precipitates out until the entiremass solidifies. The product can then be cooled, removed from the tube,and rid of residual monomer by vacuum drying. Alternatively, the productcan be dissolved in an appropriate solvent (e.g., chloroform) andrecovered by precipitation in a nonsolvent (e.g., ether-hexane mixture,3:1 v/v), and vacuum dried. Molecular weight is determined by standardmethods such as size exclusion chromatography (SEC, also known as gelpermeation chromatography or GPC). The comonomer content of the polymersis determined by nuclear magnetic resonance (NMR).

In a preferred method of synthesizing the PHAs of the present invention,the initiator is an alkylzinc alkoxide, as disclosed in the U.S. Pat.No. 5,648,452 entitled "Polymerization ofBeta-Substituted-Beta-Propiolactones Initiated by Alkylzinc Alkoxides",L. A. Schechtman and J. J. Kemper, assigned to The Procter and GambleCompany, issued Jul. 13, 1997. Such initiators have the general formulaR¹ ZnOR², wherein R¹ and R² are independently a C₁ -C₁₀ alkyl. In apreferred method of synthesis, the initiator is selected from the groupconsisting of ethylzinc isopropoxide, methylzinc isopropoxide, ethylzincethoxide, or ethylzinc methoxide; more preferably ethylzincisopropoxide.

Other copolymers useful in the present invention can be made bysubstituting the starting materials (monomers) in the above procedurewith 3-alkyl-β-lactones corresponding to the monomer units desired inthe final copolymer product.

Alternatively, biological synthesis of the biodegradable PHAs useful inthe present invention may be carried out by fermentation with the properorganism (natural or genetically engineered) with the proper feedstock(single or multicomponent). Biological synthesis may also be carried outwith botanical species genetically engineered to express the copolymersof interest (see World Patent Application No. 93-02187, Somerville,Poirier and Dennis, published Feb. 4, 1993; and U.S. Pat. No. 5,650,555,Dennis et al., issued Jul. 22, 1997, and U.S. Pat. No. 5,610,041,Nawrath et al., issued Mar. 11, 1997; and Poole, R., SCIENCE, Vol. 245,pp. 1187-1189 (1989)).

Crystallinity

The volume percent crystallinity (Φ_(C)) of a semi-crystalline polymer(or copolymer) often determines what type of end-use properties thepolymer possesses. For example, highly (greater than 50%) crystallinepolyethylene polymers are strong and stiff, and suitable for productssuch as plastic milk containers. Low crystalline polyethylene, on theother hand, is flexible and tough, and is suitable for products such asfood wraps and garbage bags. Crystallinity can be determined in a numberof ways, including x-ray diffraction, differential scanning calorimetry(DSC), density measurements, and infrared absorption. The most suitablemethod depends upon the material being tested.

X-ray diffraction is most appropriate when little is known about thethermal properties of the material and crystal structural changes mayoccur. The basic principle relies ion the fact that amorphous parts ofthe material scatter x-rays in a diffuse or broad range of angles, whilecrystals diffract x-rays into sharp, precisely defined angles. The totalscattered intensity is constant, however. This allows calculation of theamount of crystalline material in a sample if the amorphous andcrystalline diffracted intensities can be separated. A very precisemethod has been developed by Ruland, which can detect differences inpercent crystallinity as small as 2% (see Vonk, C., F. J. Balta-Calleja,X-RAY SCATTERING FROM SYNTHETIC POLYMERS, Elsevier: Amsterdam, (1989);and Alexander, L., X-RAY DIFFRACTION METHODS IN POLYMER SCIENCE, RobertKreiger Pub. Co., New York, (1979)).

Upon melting, crystals require a fixed amount of heat at the meltingtemperature transforming from crystalline to molten matter. This heat offusion can be measured by a number of thermal techniques, the mostpopular being DSC. If the heat of fusion of a 100% crystalline materialis known, and no significant annealing, or melt/recrystallisationphenomena occur upon heating to the melt, then DSC can quite accuratelydetermine weight fraction crystallinity (see THERMAL CHARACTERIZATION OFPOLYMER MATERIALS, E. Turi, Ed., Academic Press, New York, (1980); andWunderlich, B., MACROMOLECULAR PHYSICS, Academic Press, New York,(1980)).

If the densities of the pure crystalline and pure amorphous material isknown then density measurements of a material can yield the degree ofcrystallinity. This assumes additivity of specific volumes, but thisrequirement is fulfilled for polymers (or copolymers) of homogeneousstructure. This method depends on careful sample preparation so that nobubbles or large voids exist in the sample.

If purely crystalline and amorphous absorption bands can be identified,then the infrared absorption spectrum offers a convenient way ofdetermining crystallinity. (see Tadokoro, H., STRUCTURE OF CRYSTALLINEPOLYMERS, John Wiley & Sons, New York, (1979)).

It should be noted that different techniques will often give rise toslightly different values of φ_(C), because they are based on differentphysical principles. For example, density measurements often give highervalues than x-ray diffraction. This is due to the continuous changing ofthe density in the interface between crystalline and amorphous polymer(or copolymer) material. While x-ray diffraction does not detect thismatter as crystalline, density measurements will be affected by thisinterface region.

In general, PHAs of the present invention preferably have acrystallinity of from about 0.1% to about 99% as measured via x-raydiffraction; more preferably from about 2% to about 80%; more preferablystill from about 20% to about 70%.

When a PHA of the present invention is to be processed into a film, theamount of crystallinity in such PHA is more preferably from about 2% toabout 65% as measured via x-ray diffraction; more preferably from about5% to about 50%; more preferably still from about 20% to about 40%.

When a PHA of the present invention is to be processed into a sheet, theamount of crystallinity in such PHA is more preferably from about 0.1%to about 50% as measured via x-ray diffraction; more preferably fromabout 5% to about 50%; more preferably still from about 20% to about40%.

When a PHA of the present invention is to be processed into a normalfiber or a nonwoven fabric, the amount of crystallinity in such PHA ismore preferably from about 60% to about 99% as measured via x-raydiffraction; more preferably from about 70% to about 99%; morepreferably still from about 80% to about 99%.

When a PHA of the present invention is to be processed into a softelastic fiber, the amount of crystallinity in such PHA is morepreferably from about 30% to about 80% as measured via x-raydiffraction; more preferably from about 40% to about 80%; morepreferably still from about 50% to about 80%.

When a PHA of the present invention is to be processed into a moldedarticle, the amount of crystallinity in such PHA is more preferably fromabout 10% to about 80% as measured via x-ray diffraction; morepreferably from about 20% to about 70%; more preferably still from about30% to about 60%.

When a PHA of the present invention is to be processed into an elastomeror adhesive, the amount of crystallinity in such PHA is more preferablyless than about 50% as measured via x-ray diffraction; more preferablyless than about 30%; more preferably still less than about 20%.

Melt Temperature

Preferably, the biodegradable PHAs of the present invention have a melttemperature (Tm) of from about 30° C. to about 160° C., more preferablyfrom about 60° C. to about 140° C., more preferably still from about 90°C. to about 120° C.

Plastic Articles Comprising PHA

The PHAs of the present invention can be processed into a variety ofplastic articles, including but not limited to, films, sheets, fibers,foams, molded articles, nonwoven fabrics, elastomers, and adhesives.

A. Films

In one embodiment of the present invention, the plastic article is afilm. As used herein, "film" means an extremely thin continuous piece ofa substance having a high length to thickness ratio and a high width tothickness ratio. While there is no requirement for a precise upper limitof thickness, a preferred upper limit would be 0.254 mm, more preferablystill about 0.01 mm, more preferably still about 0.005 mm. Theprotective value of any film depends on its being continuous, i.e.,without holes or cracks, since it must be an efficient barrier tomolecules such as atmospheric water vapor and oxygen. The film of thepresent invention can be employed in a variety of disposable productsincluding, but not limited to, disposable diapers, shrink-wrapping(e.g., food wraps, consumer product wraps, pallet and/or crate wraps,and the like), or bags (grocery bags, food storage bags, sandwich bags,resealable "Ziploc®"-type bags, garbage bags, and the like). In apreferred embodiment of the present invention, the film of the presentinvention is liquid impervious and suitable for use in absorbentdisposable sanitary garments such as disposable diapers, femininehygiene products and the like. More preferably, films of the presentinvention, in addition to increased biodegradability and/orcompostability, have the following properties:

a) a machine direction (MD) tensile modulus from about 10,000 to about100,000 lbs./sq. in. (6.895×10⁸ dynes/sq. cm to 6.895×10⁹ dynes/sq. cm),

b) a MD tear strength of at least 70 grams per 25.4 μm of thickness,

c) a cross machine direction (CD) tear strength of at least 70 grams per25.4μ of thickness,

d) an impact strength of at least 12 cm as measured by falling balldrop,

e) a moisture transport rate less than about 0.0012 grams per squarecentimeter per 16 hours,

f) a modulus at 60° C. of at least 5.52×10⁷ dynes/sq. cm (800 lbs./sq.in), and

g) a thickness from about 12 μm to about 75 μm.

Methods for testing for such performance criteria are discussed in moredetail below.

Prior to Applicants' invention, polyhydroxyalkanoates studied for use incommercial plastics production presented significant impediments totheir use in plastics. As discussed above, polyhydroxyalkanoates such asPHB and the copolymer PHBV are difficult to process due to their thermalinstability. Furthermore, such polyhydroxyalkanoates were especiallydifficult to process into films due to their slow crystallization rate.Applicants have found that PHA copolymers of the present invention,which comprise a second RRMU as defined above having a branched alkyl ofthree (3) carbons, are surprisingly easier to process into films,especially as compared to PHB or PHBV. Applicants surprisinglydiscovered, such linear, random copolymers with a limited number ofmedium sized branched alkyl chains containing three (3) carbons,provide, in addition to biodegradability, the following properties,particularly as compared to PHB or PHBV: a) a lower melt temperature, b)a lower degree of crystallinity, and c) an improved melt rheology. Thisis especially surprising in light of the fact that the longest straightbranch of the medium sized branched alkyl chain contains only two (2)carbons.

Without being bound by theory, Applicants believe characteristics a) andb) are achieved by exclusion of the second RRMU from the crystal latticeof the first RRMU, thereby resulting in a decreased temperature forthermal processing and improved stiffness and elongation properties.Again, without being bound by theory, Applicants believe characteristicc) is achieved by increased entanglement between the copolymer chainsdue to the side chains of the second RRMU. Such increased entanglementmay occur by increased hydrodynamic volume of the copolymer (e.g., thesecond monomer unit creates kinks in the helical structure), the"hooking" or "catching" of the side chains on different copolymerbackbones while in the melt, or the decreased chain scission due to thelower Tm (i.e., the enlarged thermal process window).

1. Performance Criteria and Test Methods for Films

For a film to perform satisfactorily as a compostable disposable diaperbacksheet, it must be made of resins or structures that arebiodegradable and it must demonstrate the following properties of highstrength, adequate fluid barrier, appropriate modulus or flexibility,and adequately high melting point.

The backsheets of disposable diapers must have sufficient strength bothto process on a high speed disposable diaper converting machine and toprovide a "wetproof" barrier in use on an infant. It must besufficiently wetproof so that the clothing or bedding, either that ofthe infant or of the caregiver, is not wet or soiled. It must have amodulus or flexibility that is, at the same time, low enough to be asoft, pleasing material to be used as the outer covering of an infantdiaper yet high enough to handle easily on high speed disposable diaperconverters without wrinkling, folding, or creasing. It must havesufficient resistance to heat such that it will not deform, melt, orpermanently loose strength in typical hot storage conditions or looseits integrity on high speed disposable diaper converters which typicallyuse hot melt adhesives to bond the components of a disposable diapertogether.

Films that are sufficiently strong to be suitable as biodegradableand/or compostable backsheets for disposable diapers preferablydemonstrate two properties: (a) resistance to rupture from a droppedweight and (b) resistance to tearing in both the machine direction ofmanufacture and the cross-machine direction of manufacture. Preferredbacksheets of the present invention can withstand the drop of aspherical steel ball of about 19 millimeters in diameter and 27.6 to28.6 gram mass from a height of 12 centimeters so that at least 50% ofthe tests result in no rupture of any size (deformation is acceptable).Preferred materials are those that exhibit 50% or less failures from aheight of more than 20 centimeters. Similarly, acceptable backsheets ofthe present invention demonstrate an average tear propagation resistanceof 70 grams per 25.4 micron thickness of material in both the machinedirection and cross-machine direction of manufacture when a standardElmendorf pendulum-type test device, such as Elmendorf Model No. 60-100,is employed against 16 plies of material which have been prepared with acut or notch according to TAPPI Method T 414om-88. More preferable arethose backsheets that demonstrate tear propagation resistances of 200 ormore grams per 25.4 micron thickness in the cross-machine directionbecause these are particularly good at avoiding a tendency to fail inuse by splitting.

It has also been found that films of sufficient barrier to moisturetransport are those that permit less than 0.0012 grams of syntheticurine to pass into an absorbent paper towel per square centimeter ofarea per 25.4 micron thickness for every 16 hours of time when the testfilm is located between the absorbent paper towel and a typicalabsorbent gelling material-containing diaper core and a pressuresimulating that of a baby. The specific conditions of the test are thatthe area of the core is larger than that of the test material, the coreis loaded with synthetic urine to its theoretical capacity and it isunder a weight of about 35 g/cm² (0.5 psi).

It has also been found that materials of sufficient heat resistancedemonstrate a Vicat softening point of at least 45° C. Vicat softeningis tested using a Heat Distortion Apparatus Model No. CS-107 orequivalent and a modification of ASTM D-1525. The modification is in thepreparation of the sample. A 19 square millimeter size film of 4.5 to6.5 mm thickness is prepared for Vicat needle penetration tests bymelting the material to be tested into a mold using a temperature of120° C. and pressure of 7.031×10⁵ g/cm² (10,000 psi) (using a Carver orsimilar press) for two minutes after a warm-up period of at least 2minutes. The Vicat softening point is the temperature at which aflat-ended needle of 1 sq. mm circular cross section will penetrate thesample to a depth of 0.1 cm under a load 1000 g using a uniformtemperature rise rate of 50° C. per hour.

It has also been found that materials of sufficient machine directionmodulus demonstrate a 1% secant-type modulus above at least about6.895×10⁸ dynes/cm² (10,000 psi) and below about 6.895×10⁹ dynes/cm²(100,000 psi). The test is performed on an electronic tensile testmachine such as the Instron Model 4201. A 2.54 cm wide strip ofmaterial, preferably of 0.00254 cm in thickness, is cut to a length ofabout 30 cm with the longer dimension parallel to the machine directionof the material. The test strip is clamped into the jaws of the tensiletestor so that the gauge or actual length of the material tested is 25.4cm The jaws are separated at a slow speed in the range of 2.54 cm perminute to 25.4 cm per minute and a stress-strain curve is plotted on achart within an attached recording device. The 1% secant modulus isdetermined by reading the stress or tensile from the chart at the 1%elongation strain point. For example, the 1% strain point is achievedwhen the distance between jaws has increased by 0.254 cm. When the jawsare separating at the rate of 2.54 cm per minute and the recordingdevice is running at a speed of 25.4 cm per minute, the 1% strain pointwill be located at a distance of 2.54 cm from the initial point. Thetensile response is divided by the thickness of the sample material ifit is not 0.00254 cm in thickness. Particularly soft, and thereforepreferred, materials exhibit 1% secant moduli in the range of 6.895×10⁸to 2.068×10⁹ dynes/cm² (10,000 to 30,000 psi).

Since absorbent articles may experience temperatures as high as 140° F.(60° C.) during warehouse storage or shipping in trucks or railcars, itis important that the backsheet film and other components retain theirintegrity at these temperatures. Although it is expected that themodulus of the films will decrease somewhat between 20° C. and 60° C.,the modulus should not decrease too far and allow the film to deform inthe package before it reaches the end user.

For example, a polyethylene backsheet with a room temperature modulus ofabout 4×10⁹ dynes/cm² (58,000 psi) may have a 60° C. modulus of 1.2×10⁹dynes/cm² (18,560 psi) which is acceptable. A softer polyethylenebacksheet with a room temperature modulus of about 8.0×10⁸ dynes/cm²(11,600 psi) may have a 60° C. modulus of about 3.5×10⁸ dynes/cm² (5,076psi) which is still acceptable. In general, an acceptable backsheet filmof the present invention will have a 60° C. modulus of at least 5.52×10⁷dynes/cm² (800 psi).

The modulus dependence on temperature, also called a modulus/temperaturespectrum, is best measured on a dynamic mechanical analyzer (DMA) suchas a Perkin Elmer 7 Series/Unix TMA 7 Thermomechanical Analyzer equippedwith a 7 Series/Unix DMA 7 Temperature/Time software package,hereinafter referred to as the DMA 7, available from the Perkin-ElmerCorporation of Norwalk, Conn. Many other types of DMA devices exist, andthe use of dynamic mechanical analysis to study the modulus/temperaturespectra of polymers is well known to those skilled in the art of polymer(or copolymer) characterization. This information is well summarized intwo books, the first being DYNAMIC MECHANICAL ANALYSIS OF POLYMERICMATERIAL, MATERIALS SCIENCE MONOGRAPHS VOLUME 1 by T. Murayama (ElsevierPublishing Co., 1978) and the second being MECHANICAL PROPERTIES OFPOLYMERS AND COMPOSITES, VOLUME 1 by L. E. Nielsen (Marcel Dekker,1974).

The mechanism of operation and procedures for using the DMA 7 are foundin Perkin-Elmer Users' Manuals 0993-8677 and 0993-8679, both dated May,1991. To those skilled in the use of the DMA 7, the following runconditions should be sufficient to replicate the 60° C. modulus datapresented hereinafter.

To measure the modulus/temperature spectrum of a film specimen, the DMA7 is set to run in temperature scan mode and equipped with an extensionmeasuring system (EMS). A film specimen approximately 3 mm wide, 0.0254mm thick, and of sufficient length to allow 6 to 8 mm of length betweenthe specimen grips is mounted in the EMS. The apparatus is then enclosedin an environmental chamber swept continuously with helium gas. Stressis applied to the film in the length direction to achieve a deformationor strain of 0.1 percent of the original length. A dynamic sinusoidalstrain is applied to the specimen at a frequency of 5 cycles per second.In the temperature scan mode, the temperature is increased at a rate of3.0° C./minute from 25° C. to the point where the specimen melts orbreaks, while the frequency and stress are held constant.Temperature-dependent behavior is characterized by monitoring changes instrain and the phase difference in time between stress and strain.Storage modulus values in Pascals are calculated by the computer alongwith other data and displayed as functions of temperature on a videodisplay terminal. Normally the data are saved on computer disk and ahard copy of the storage modulus/temperature spectrum printed forfurther review. The 60° C. modulus is determined directly from thespectrum.

2. Method of Film Manufacture

The films of the present invention used as backsheets having increasedbiodegradability and/or compostability may be processed usingconventional procedures for producing single or multilayer films onconventional film-making equipment. Pellets of the PHAs of the presentinvention can be first dry blended and then melt mixed in a filmextruder. Alternatively, if insufficient mixing occurs in the filmextruder, the pellets can be first dry blended and then melt mixed in aprecompounding extruder followed by repelletization prior to filmextrusion.

The PHAs of the present invention can be melt processed into films usingeither cast or blown film extrusion methods both of which are describedin PLASTICS EXTRUSION TECHNOLOGY--2nd Ed., by Allan A. Griff (VanNostrand Reinhold--1976). Cast film is extruded through a linear slotdie. Generally the flat web is cooled on a large moving polished metalroll. It quickly cools, and peels off this first roll, passes over oneor more auxiliary cooling rolls, then through a set of rubber-coatedpull or "haul-off" rolls, and finally to a winder. A method of making acast backsheet film for the absorbent articles of the present inventionis described in an example below.

In blown film extrusion, the melt is extruded upward through a thinannular die opening. This process is also referred to as tubular filmextrusion. Air is introduced through the center of the die to inflatethe tube and thereby causing it to expand. A moving bubble is thusformed which is held at a constant size by control of internal airpressure. The tube of film is cooled by air, blown through one or morechill rings surrounding the tube. The tube is then collapsed by drawingit into a flattening frame through a pair of pull rolls and into awinder. For backsheet applications the flattened tubular film issubsequently slit open, unfolded, and further slit into widthsappropriate for use in products.

Both cast film and blown film processes can be used to produce eithermonolayer or multilayer film structures. For the production of monolayerfilms from a single thermoplastic material or blend of thermoplasticcomponents only a single extruder and single manifold die are required.

For the production of multilayer films of the present invention,coextrusion processes are preferably employed. Such processes requiremore than one extruder and either a coextrusion feedblock ormulti-manifold die system or combination of the two to achieve themultilayer film structure.

U.S. Pat. Nos. 4,152,387, and 4,197,069, disclose the feedblockprinciple of coextrusion. Multiple extruders are connected to thefeedblock which employs moveable flow dividers to proportionally changethe geometry of each individual flow channel in direct relation to thevolume of polymer passing through said flow channels. The flow channelsare designed such that at their point of confluence, the materials flowtogether at the same flow rate and pressure eliminating interfacialstress and flow instabilities. Once the materials are joined in thefeedblock, they flow into a single manifold die as a compositestructure. It is important in such processes that the melt viscositiesand melt temperatures of the materials do not differ too greatly;otherwise flow instabilities can result in the die leading to poorcontrol of layer thickness distribution in the multilayer film.

An alternative to feedblock coextrusion is a multi-manifold or vane dieas disclosed in aforementioned U.S. Pat. Nos. 4,152,387, 4,197,069, andin U.S. Pat. No. 4,533,308. Whereas in the feedblock system melt streamsare brought together outside and prior to entering the die body, in amulti-manifold or vane die each melt stream has its own manifold in thedie where the polymers spread independently in their respectivemanifolds. The melt streams are married near the die exit with each meltstream at full die width. Moveable vanes provide adjustability of theexit of each flow channel in direct proportion to the volume of materialflowing through it, allowing the melts to flow together at the samelinear flow rate, pressure, and desired width.

Since the melt flow properties and melt temperatures of the processedmaterials may vary widely, use of a vane die has several advantages. Thedie lends itself toward thermal isolation characteristics whereinmaterials of greatly differing melt temperatures, for example up to 175°F. (80° C.), can be processed together.

Each manifold in a vane die can be designed and tailored to a specificpolymer (or copolymer). Thus the flow of each polymer is influenced onlyby the design of its manifold, and not by forces imposed by otherpolymers. This allows materials with greatly differing melt viscositiesto be coextruded into multilayer films. In addition, the vane die alsoprovides the ability to tailor the width of individual manifolds, suchthat an internal layer, for example a water soluble biodegradablepolymer like Vinex 2034, can be completely surrounded by water insolublematerials leaving no exposed edges susceptible to water. Theaforementioned patents also disclose the combined use of feedblocksystems and vane dies to achieve more complex multilayer structures.

The multilayer films of the present invention may comprise two or morelayers. In general, balanced or symmetrical three-layer and five-layerfilms are preferred. Balanced three-layer multilayer films comprise acenter core layer and two identical outer layers, wherein said centercore layer is positioned between said two outer layers. Balancedfive-layer multilayer films comprise a center core layer, two identicaltie layers, and two identical outer layers, wherein said center corelayer is positioned between said two tie layers, and a tie layer ispositioned between said center core layer and each outer layer. Balancedfilms, though not essential to the films of the present invention, areless prone to curling or warping than unbalanced multilayer films.

In three layer films, the center core layer may comprise 30 to 80percent of the films' total thickness and each outer layer comprises 10to 35 percent of the films' total thickness. Tie layers, when employed,each comprise from about 5 percent to about 10 percent of the films'total thickness.

B. Sheets

In another embodiment of the present invention, the plastic article is asheet. As used herein, "sheet" means a very thin continuous piece of asubstance, having a high length to thickness ratio and a high width tothickness ratio, wherein the material is thicker than 0.254 mm. Sheetingshares many of the same characteristics as film in terms of propertiesand manufacture, with the exception that sheeting is stiffer, and has aself-supporting nature. Such differences in stiffness and support resultin some modification of the manufacturing methods.

1. Methods of Manufacture

Sheets, because of thickness and consequent stiffness, cannot be blownas a film. However many other of the same processes used to make filmcan be modified to make sheeting. One example is cast extrusion which isdescribed previously. In addition to extrusion, sheeting is also madevia rolling and calendering.

a. Rolling

Rolling produces a film with predominately machine direction orientationby accelerating the film from a nip point where the thickness is reduced(ENCYCLOPEDIA OF POLYMER SCIENCE AND ENGINEERING, Vol. 8, pp. 88-106,John Wiley and Sons, New York, (1986); hereinafter referred to as"EPSE-1"). Large forces are found at the nip point, but overallorientation can be increased over other forms of machine directionorientation.

b. Calendering

To produce an unoriented cast film or sheet with high throughput,calendering is used (G. W. Eghmy, Jr. in MODERN PLASTICS, J. Agrandoff,ed. Encyclopedia, Vol 59(10A), pp. 220-222 (1982) and R. A. Elden and A.D. Swan, CALENDERING OF PLASTICS, American Elsevier Co., Inc., New York,(1971)). The calendering process employs stacks of specially hardened,driven rolls, supported in a manner so they may be bent or skewed inposition relative to each other during operation. This is to controlthickness in the calendered material. Calenders are usually made up offour rolls that form three nips. These nips are the feed, metering andfinishing nips. The feed nip is where the polymer is supplied, mixed,and heated. The metering nip reduces the thickness of the sheet to theapproximate final thickness. The finishing nip adjusts the gauge of thesheet by varying the position of the third or middle roll. (see EPSE-2)

C. Fibers

In another embodiment of the present invention, the plastic article is afiber. As used herein, "fiber" refers to a flexible, macroscopicallyhomogeneous body having a high length-to-width ratio and a small crosssection. A general overview of fibers can be found in the ENCYCLOPEDIAOF POLYMER SCIENCE AND ENGINEERING, Vol. 6, p. 647-755 and pp. 802-839,John Wiley and Sons, New York, (1986) (hereinafter referred to as"EPSE-2"). The fibers of the present invention are useful as textiles inyarns for garments. The fibers of the present invention are also usefulfor manufacturing lightweight fibrous materials useful in agriculturalapplications to protect, promote, or control plant growth. They are alsoused in green house thermal screens, crop row covers, turf covers, weedbarriers and hydroponics. Key properties are light, air, and moisturepermeability. An important aspect is cost effectiveness when consideredin terms of weight, strength, and dimension stability.

An elastomeric fiber is a fiber that consists of polymers (orcopolymers) with a main glass transition temperature much below roomtemperature (see EPSE-2). This criterion excludes some fibers withelastic properties, such as crimped hard fibers, but allows inclusion ofmulti-constituent fibers where one of the constituents is an elastomer.All elastomeric fibers are characterized by a higher elongation atbreak, lower modulus, and higher recovery from large deformation thannormal fibers.

1. Methods of Fiber Manufacture

The fibers of the present invention may be processed using a variety ofconventional techniques well-known in the art including, but not limitedto, melt spinning, dry spinning, and wet spinning. Combinations of thesethree basic processes are often used.

In melt spinning a PHA of the present invention is heated above itsmelting point and the molten PHA is forced through a spinneret. Aspinneret is a die with many small orifices which are varied in number,shape and diameter (see EPSE-2). The jet of molten PHA is passed througha cooling zone where the PHA solidifies and is then transferred topost-drawing and take-up equipment.

In dry spinning, a PHA of the present invention is dissolved and the PHAsolution is extruded under pressure through a spinneret (see EPSE-2).The jet of PHA solution is passed through a heating zone where thesolvent evaporates and the filament solidifies.

In wet spinning, a PHA of the present invention is also dissolved andthe solution is forced through a spinneret which is submerged in acoagulation bath (see ESPE-2). As the PHA solution emerges from thespinneret orifices within the coagulation bath, the PHA is eitherprecipitated or chemically regenerated. Usually, all these processesneed further drawing for useful properties to be obtained, for exampleto serve as textile fibers. "Drawing" refers to stretching andattenuation of fibers to achieve an irreversible extension, inducemolecular orientation, and develop a fiber-fine structure (see ESPE-2).This fine structure is characterized by a high degree of crystallinityand by orientation of both the crystallites and the amorphous PHA chainsegments.

D. Foams

In another embodiment of the present invention, the plastic article is aflexible foam. As used herein, "foam" refers PHA of the presentinvention whose apparent density has been substantially decreased by thepresence of numerous cells distributed throughout its bulk (see ASTM D883-62T, American Society for Testing and Materials, Philadelphia, Pa.,(1962)). Such two-phase gas/solid systems in which the solid iscontinuous and composed of a synthetic polymer or rubber includecellular polymers (or copolymers), expanded plastics and foamed plastics(ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Vol. 11, John Wiley & Sons, NewYork (1980), hereinafter referred to as "ECT").

The gas phase is distributed into pockets or voids called cells whichare classified into two types, open and closed. Open-celled material arefoams whose cells are inter-connected such that gases may pass freelythrough the cells. Closed-cell materials have cells that are discreteand isolated from each other.

Foams are further categorized into flexible and rigid foams. Thisclassification is based on a particular ASTM test procedure (see ASTM D,Vol. 37, pp. 1566-1578, American Society of Testing and Materials,Philadelphia, Pa., (1978)). A flexible foam is a foam which does notrupture when a 20×2.5×2.5 cm piece is wrapped around a 2.5 cm mandrel ata uniform rate of 1 lap/5 s at 15-25° C. Foams that do rupture underthis test are referred to as rigid foams.

Foams find many applications as packaging, comfort cushioning,insulation, and structural components. In the some areas of packaging afoamed material having increased biodegradability and/or compostabilitywould offer superior benefits to currently used packaging such aspolystyrene, paper and starch foams. In hot food containers, polystyreneoffers significantly higher thermal insulation over the only currentlydegradable alternative, paper wraps. Foamed articles comprising a PHA ofthe present invention have the thermal insulating properties ofpolystyrene, yet are biodegradable and/or compostable. These materialsare ideal for hot food take-out and cold food packaging.

Foamed polystyrene chips are used as cushioned packing materials forconsumer and industrial goods. Many of these chips end up in landfills.Foamed chips comprising a PHA of the present invention perform as wellas polystyrene and have increased biodegradability and/orcompostability. Unlike other compostable packaging material such asstarch, such PHA chips are resistant to many common solvents and liquidsincluding water.

1. Methods of Foam Manufacture

The foams of the present invention may be processed using conventionalprocedures well-known to those skilled in the art. A predominant methodof foam production involves expanding a fluid polymer (or copolymer)phase to a low density cellular phase and then preserving this state(see ECT). Other processes include leaching out materials that have beenpreviously dispersed in the polymer (or copolymer), sintering smallparticles and dispersing cellular particles in a polymer (or copolymer).Three steps make up the expansion process. These are cell initiation,cell growth and cell stabilization. Many methods are used to create,grow, and stabilize cells.

Expandable formulations rely on increasing the pressure within theinitiated cells relative to that of the surroundings. The cells arestabilized by either chemical (e.g. crosslinking, polymerization) orphysical means (crystallization, melt-glass transition). Polystyrene isan example of a polymer that is foamed by of this kind of process. Ablowing agent such as isomeric pentanes and hexanes or halocarbons (H.R. Lasman, MODERN PLASTICS, Vol. 42(1A), p. 314 (1964)) is mixed withthe polymer (or copolymer) either by heating and allowing the blowingagent to penetrate the polymer (U.S. Pat. No. 2,681,321, issued Jun. 15,1954, F. Stastny and R. Gaeth, assigned to BASF), or by polymerizing thepolystyrene in the presence of the blowing agent (U.S. Pat. No.2,983,692, issued May 9, 1961, G. F. D'Alelio, assigned to Koppers Co.).Fabrication of articles are usually carried out in multiple steps, thefirst of which uses steam, hot water or hot air to expand the polymerinto low density preformed beads. These preformed beads are aged,sometimes in multiple steps for correct cell size, and then packed intomolds and fused together by heat and further expansion (S. J. Skinner,S. Baxter, and P. J. Grey, Trans. J. PLAST. INST. Vol. 32, p. 180(1964)). Stabilization is accomplished by cooling the polymer totemperatures below its glass transition temperature.

Decompression expansion processes create and grow cells by lowering theexternal pressure during processing. Cellular polyethylene andpolypropylene are often made in this manner. A decomposing blowing agentis premixed with the polymer (or copolymer) and fed through an extruderunder elevated temperature and pressure such that the blowing agentpartially decomposes. When the material exits the extruder, it enters alower pressure zone. Simultaneous expansion and cooling take place,resulting in a stable cellular structure owing to rapid crystallizationof the polymer (R. H. Hansen, SPE J., Vol.18, p. 77 (1962), W. T.Higgins, MOD. PLAST., Vol. 31(7), p. 99, (1954)).

Dispersion processes produce foams by directing dispersing solid or gasinto the polymer (or copolymer) phase and then, when necessary,stabilizing the mixture (ECT). In one such process, frothing, a gas ismechanically dispersed in the polymer or monomer phase, producing a foamof temporary stability. This foam is then chemically stabilized bycrosslinking or polymerization. Latex foam rubber is manufactured inthis way (see ECT).

E. Molded Articles

In another embodiment of the present invention, the plastic article is amolded article. As used herein, "molded article" means objects that areformed from polymer or copolymer materials (e.g., PHA) which areinjected, compressed, or blown by means of a gas into shape defined by afemale mold. These objects can be solid objects like toys, or hollowlike bottles and containers.

Injection molding of thermoplastics is a multi-step process by which aPHA of the present invention is heated until it is molten, then forcedinto a closed mold where it is shaped, and finally solidified bycooling. There are a variety of machines that are used in injectionmolding. Three common types are ram, screw plasticator with injection,and reciprocating screw devices (see ENCYCLOPEDIA OF POLYMER SCIENCE ANDENGINEERING, Vol. 8, pp. 102-138, John Wiley and Sons, New York, (1986);hereinafter referred to as "EPSE-3"). A ram injection molding machine iscomposed of a cylinder, spreader, and plunger. The plunger forces themelt in the mold. A screw plasticator with a second stage injectionconsists of a plasticator, directional valve, a cylinder without aspreader, and a ram. After plastication by the screw, the ram forces themelt into the mold. A reciprocating screw injection machine is composedof a barrel and a screw. The screw rotates to melt and mix the materialand then moves forward to force the melt into the mold.

Compression molding in thermoplastics consists of charging a quantity ofa PHA of the present invention in the lower half of an open die. The topand bottom halves of the die are brought together under pressure, andthen molten PHA conforms to the shape of the die. The mold is thencooled to harden the plastic (see EPSE-3).

Blow molding is used for producing bottles and other hollow objects (seeEPSE-3). In this process, a tube of molten PHA known as a parison isextruded into a closed, hollow mold. The parison is then expanded by agas, thrusting the PHA against the walls of a mold. Subsequent coolinghardens the plastic. The mold is then opened and the article removed.

Blow molding has a number of advantages over injection molding. Thepressures used are much lower than injection molding. Blow molding canbe typically accomplished at pressures of 25-100 psi between the plasticand the mold surface. By comparison, injection molding pressures canreach 10,000 to 20,000 psi (see EPSE-3). In cases where the PHA has ahave molecular weights too high for easy flow through molds, blowmolding is the technique of choice. High molecular weight polymers (orcopolymers) often have better properties than low molecular weightanalogs, for example high molecular weight materials have greaterresistance to environmental stress cracking. (see EPSE-3). It ispossible to make extremely thin walls in products with blow molding.This means less PHA is used, and solidification times are shorter,resulting in lower costs through material conservation and higherthroughput. Another important feature of blow molding is that since ituses only a female mold, slight changes in extrusion conditions at theparison nozzle can vary wall thickness (see EPSE-3). This is anadvantage with structures whose necessary wall thicknesses cannot bepredicted in advance. Evaluation of articles of several thicknesses canbe undertaken, and the thinnest, thus lightest and cheapest, articlethat meets specifications can be used.

F. Nonwovens

In another embodiment of the present invention, the plastic article is anonwoven. As used herein "nonwoven" means porous, textile likematerials, usually in flat sheet form, composed primarily, or entirely,of fibers assembled in webs that are manufactured by processes otherthan spinning, weaving, or knitting. A general overview of nonwovenfabrics can be found in the ENCYCLOPEDIA OF POLYMER SCIENCE ANDENGINEERING, Second Edition, Vol. 10, pp. 204-226 (referred to hereafteras "EPSE-4"). Other names for these materials are bonded fabrics, formedfabrics, or engineered fabrics. The thickness of the fabric sheets mayvary from 25 mm to several centimeters, and the weight from 10 g/m² to 1kg/m². Nonwoven fabrics have a wide range of physical propertiesdepending on the material and process used in forming the web. A fabricmay be self-supporting and stiff as paper or drapable as a conventionalcloth fabric.

In contrast to conventional textiles, the fundamental structure of allnonwovens is a web of fibers arranged more or less randomly (NONWOVENSIND., Vol. 17, p. 36 (March 1986), NONWOVENS WORLD, Vol. 1, p. 36(May-June 1986)). Thus, the key element is the single fiber. Tensile,tear, and tactile properties in the nonwoven arise from adhesive orother chemical and physical bonding, fiber-to-fiber friction created byentanglement, and reinforcement by other materials such as foams andfilms (see EPSE-4).

1. Method of Manufacture of Nonwoven Fabrics

The nonwoven fabrics of the present invention may be made byconventional techniques known in the art. The production of nonwovenfabrics involves: 1) making fibers of various lengths and diameters; 2)creating a web of these fibers; and 3) bonding of fibers within the webby adhesive, or mechanical-frictional forces created by fiber contact orentanglement. In addition to these steps, reinforcing the web by forminga composite with other materials (e.g., yarns, scrims, films, nettings,and unbonded webs) is sometimes preferred. Variations of one or severalof these steps allows for the enormous range of nonwoven fiber types.The term "staple fibers" was originally applied to fibers of naturalorigin long enough to be processed on textile machinery, but excludingendless filaments, eg, silk. In the present context, as applied to PHAof the present invention, "staple fibers" are of relatively uniformlength, ca. 1.3-10.2 cm, with a regular crimp i.e., a three-dimensionalwavelike shape. Regenerated and other extruded fibers are endless asformed. They are cut during the manufacturing process to a specifiedlength to meet a processing or market need. Extruded fibers are alsoproduced as continuous filaments without crimp. The processes forforming webs from staple fibers are different from those usingcontinuous filaments. The products obtained from staple and filamentfiber webs may differ substantially in properties (see EPSE-4).

The mechanical properties of the fibers as defined by their chemicalcomposition, determine the ultimate properties of the fabric. Webstructure and bonding maximize inherent fiber characteristics (seeEPSE-4). Other materials that may be used in the nonwovens of thepresent invention in combination with the PHA are wood pulp; regeneratedfibers including viscose rayon and cellulose acetate; and syntheticfibers like poly(ethylene terephthalate) (PET), nylon-6, nylon 6,6,polypropylene (PP), and poly(vinyl alcohol). Facings of disposablediapers or sanitary napkins made from PHA nonwoven fabrics of thepresent invention preferably feel dry even when the absorbent, innerabsorbent layer is saturated. Important fiber characteristics thataffect performance include length, diameter, density, crimp, crosssection shape, spin-finish (lubricant that is added to the surface ofextruded fibers to enhance processability), delustering (small amountsof TiO₂ pigment added before extrusion to increase whiteness or toreduce sheen) and the draw ratio.

a. Web-making Methods

The characteristics of the fiber web determine the physical propertiesof the final product. These characteristics depend largely on fiberarchitecture, which is determined by the mode of web formation. Fiberarchitecture includes the predominant fiber direction, whether orientedor random, fiber shape (straight, hooked, or curled), the extent ofinterfiber engagement or entanglement, crimp, and compaction(web-density control). Web characteristics are also influenced by fiberdiameter, length, web weight, and chemical and mechanical properties ofthe polymer (see EPSE-4).

The choice of method for forming the web is determined by fiber length.Initially, the methods for forming webs from staple-length fibers(fibers long enough to be handled by conventional spinning equipment,usually from about 1.2 to about 20 cm long, but not endless) are basedon the textile-carding process, whereas web formation from short fibersis based on papermaking technologies. Although these technologies arestill in use, other methods have been subsequently developed. Forexample, webs are formed from long, virtually endless filaments directlyfrom bulk polymer; both web and fibers are produced simultaneously (seeEPSE-4). A variety of web-making methods are known, including carding,air-laying, wet-forming, spinbonding, and meltblowing.

The carding process is derived from the ancient manual methods of fibercarding, where natural staple fibers were manipulated by beds ofneedles. In carding, clumps of staple fibers are separated mechanicallyinto individual fibers and formed into a coherent web by the mechanicalaction of moving beds of closely spaced needles.

In the air-laying process, the orientation created by carding iseffectively improved by capturing fibers on a screen from an airstream(see U.S. Pat. No. 3,338,992, G. A. Kinney, assigned to E.I. du Pont deNemours & Co., Inc., issued Aug. 29, 1967). The fibers are separated byteeth or needles and introduced into an airstream. Total randomizationwould exclude any preferential orientation when the fibers are collectedon the screen.

Wet-forming processes employ very short fibers. Initially, webs areformed from short fibers by modified papermaking techniques. The fibersare continuously dispersed in a large volume of water and caught on amoving endless wire screen. Once the web is caught on the screen, it istransferred to belts or felts and dried on heated drums (see EPSE-4).

The spunbonded web process involves making fibers and websimultaneously, directly from bulk polymer. The bulk polymer is melted,extruded, and drawn (often by triboelectric forces) to filaments thatare randomized and deposited onto belts as a continuous web. Thefilaments are virtually endless. The spunbond process produces webs oflow crimp filaments in the normal diameter range of about 1.7 dtex (1.5den) or slightly higher. The birefringence and uniformity of diameter ofthese filaments are similar to standard textile fibers and filaments(see EPSE-4). Each production line is suitable for a specific polymerand a single-bonding system (see U.S. Pat. No. 4,163,305 (Aug. 7, 1979),V. Semjonow and J. Foedrowitz (to Hoechst AG)).

Webs are also made directly from bulk polymers by the meltblown process(see U.S. Pat. No. 3,322,607, S. L. Jung, assigned to E.I. duPont deNemours & Co., Inc., May 30, 1967). The molten PHA is forced throughvery fine holes in a special die into a high velocity airstream wherethe PHA is formed into very fine, although irregular, filaments ofindeterminate lengths. The filaments are simultaneously formed into aweb where melting and resolidification, and possibly static forces, holdthem together (see EPSE-4). The web consists primarily of filaments withvery fine diameters.

b. Web bonding

The bonding of fibers gives the strength to the web and influences otherproperties. Both adhesive and mechanical means are used. Mechanicalbonding employs the engagement of fibers by frictional forces. Bondingcan also be achieved by chemical reaction, i.e., formation of covalentbonds between binder and fibers (see EPSE-4).

G. Elastomers

In another embodiment of the present invention, the plastic article isan elastomer. As used herein "elastomer" refers to materials whichexhibit both long-range deformability on application of stress andessentially complete recovery on removal. A general discussion onelastomers can be found in the Encyclopedia of Polymer Science andEngineering, Second Edition, Vol. 5, pp. 106-127 (hereafter referred toas "EPSE-5"). Preferably, an elastomer of the present invention, at roomtemperature, can be stretched repeatedly to at least twice its originallength and, after removal of the tensile load, will immediately andforcibly return to approximately its original length. Elastomers of thepresent invention are above the glass-transition temperature Tg andamorphous in the unstressed state to exhibit high local segmentalmobility necessary for deformation. The chains are flexible andintermolecular (interchain) forces are weak. The elastomers of thepresent invention possess a sufficient number of chemical or physicalcross-links to form a continuous network in order to restrain chainslippage.

Thermoplastic elastomers of the present invention have many of theproperties of conventional elastomers such as vulcanized rubbers, butare processed as thermoplastics rather than thermosets. Transition froma fluid melt to a solid is reversible. Thermoplastic elastomers of thepresent invention are multiphase systems, where at least one phase issoft and rubbery and another hard. With thermoplastic elastomers, thetransition from a processible melt to a solid, rubberlike object israpid and reversible and takes place upon cooling. Preferably, PHAs ofthe present invention which are processed into an elastomer havesufficiently high branch content to enable them to act as thermoplasticelastomers, with the crystalline areas acting as the hard segment andthe amorphous segments acting as the soft segment. Thermoplasticelastomers of the present invention can be processed on conventionalplastics equipment, such as injection molders.

Important structural parameters for thermoplastic elastomers are themolecular weight, the nature of the soft and hard segments, and theratio of soft to hard segments. The ratio of hard to soft segmentseffects the total modulus of the elastomer, increasing with theproportion of the hard segments.

Elastomers of the present invention comprising a PHA of the presentinvention can also be used in blend formulations with other polymers (orcopolymers), even non-elastomeric PHAs, to increase impact strength andtoughness in stiffer materials.

H. Adhesive

In another embodiment of the present invention, the plastic article isan adhesive. As used herein "adhesive" means a material that joins twoother materials, called adherends, together. A general discussion onadhesives can be found in the Encyclopedia of Polymer Science andEngineering, Vol. 1, pp. 547-577, (hereafter referred to as "EPSE-6").In one embodiment of the present invention, the adhesive is applied as aliquid, preferably of a low viscosity. In the liquid form the adhesivewets the adherend surface and flows into the crevices in the adherendsurfaces. The liquid form of the adhesive is obtained by heating to thepoint that flow occurs, dissolving or dispersing the material in asolvent, or starting with liquid monomers or oligomers that polymerizeor react after application. The adhesive then undergoes a phase changeto a solid either by cooling, solvent evaporation, or reaction, in orderfor the joint to acquire the necessary strength to resist shearingforces. However, pressure-sensitive adhesives are an exception, since nophase change occurs.

The PHAs of the present invention may be processed into a variety ofadhesives, including but not limited to, hot melt, solution, dispersionand pressure sensitive adhesives.

1. Hot-melt Adhesives

As used herein, "hot-melt adhesive" refers to a thermoplastic polymer orcopolymer (e.g., a PHA of the present invention) that is heated toobtain a liquid of flowable viscosity, and, after application, cooled toobtain a solid. Generally, the molecular weight of the adhesive istailored to provide flowability in the melt, but still be strong enoughin the solid form to resist shearing forces experienced in theapplication. Due to their thermoplastic properties, the PHAs of thepresent invention are particularly useful as hot-melt adhesives. Theprimary feature of hot-melt adhesives is the ability of thethermoplastic material to flow above a certain temperature, high abovethe normal use temperature of the bond. Upon cooling, the materialhardens, either through passing through the glass transition temperatureof one of the components, or the crystallization temperature. Thishardening lends physical integrity to the bond. In PHAs, the mode ofsolidification is crystallization.

2. Solutions and Dispersions

The adhesives of the present invention may be applied either assolutions, in water or an organic solvent, or in the form of aqueousdispersions. In either form, the solvent must be removed afterapplication for the adhesive to attain the required solid form. Thesolution or dispersion is usually applied to one of the surfaces to bebonded, and the solvent removed before the second surface is joined;often, heating is required to expedite the drying step. With poroussubstrates, such as paper or wood, final drying can take place afterformation of the joint. Solids contents of the solutions vary from 5 to95%, although values from 20 to 50% are most common.

As used herein, "dispersion" refers to when adhesives are prepared bytrue emulsion polymerization or dispersed as larger particles in somecarrier fluid. In addition to their economic advantage, dispersionscontaining 40-50% solids offer lower viscosity than solutions, even ifthe solids are high molecular-weight polymers (EPSE-6). Adhesivedispersions of the present invention may be prepared by high shear inthe presence of surfactants to obtain waterborne formulations,procedures which are well known to those skilled in the art.

3. Pressure-sensitive Adhesives

Another type of adhesive of the present invention is apressure-sensitive adhesive. Unlike other adhesives, thepressure-sensitive adhesives do not change their physical state from theinitial application, to the final breaking of the adhesive bond. Theyremain permanently deformable, and may alter under even slightapplication of pressure. They are adhesives that in dry form arepermanently tacky at room temperature and that firmly adhere to surfacesupon mere contact. The most common form of pressure-sensitive adhesiveis on a backing, usually in tape form. Common masking tape, for example,is manually applied after the user removes the desired length from aroll. Many bandages are held to the skin by pressure-sensitiveadhesives.

Disposable Personal Care Products

The present invention further relates to disposable personal careproducts comprising a PHA of the present invention. For example,compostable absorbent articles comprising a liquid pervious topsheet, aliquid impervious backsheet comprising a film of the present invention(i.e., a film comprising a PHA of the present invention), and anabsorbent core positioned between the topsheet and backsheet. Suchabsorbent articles include infant diapers, adult incontinent briefs andpads, and feminine hygiene pads and liners.

Additional personal care products comprising a PHA of the presentinvention include personal cleansing wipes; disposable health careproducts such as bandages, wound dressings, wound cleansing pads,surgical gowns, surgical covers, surgical pads; other institutional andhealth care disposables such as gowns, wipes, pads, bedding items suchas sheets and pillowcases, foam mattress pads.

A. Absorbent Articles

Films of the present invention used as liquid impervious backsheets inabsorbent articles of the present invention, such as disposable diapers,typically have a thickness of from 0.01 mm to about 0.2 mm, preferablyfrom 0.012 mm to about 0.051 mm.

In general, the liquid impervious backsheet is combined with a liquidpervious topsheet and an absorbent core positioned between the topsheetand the backsheet. Optionally, elastic members and tape tab fastenerscan be included. While the topsheet, the backsheet, the absorbent coreand elastic members may be assembled in a variety of well knownconfigurations, a preferred diaper configuration is described generallyin U.S. Pat. No. 3,860,003, entitled "Contractible Side Portion forDisposable Diaper" which issued to Kenneth B. Buell on Jan. 14, 1975.

The topsheet is preferably, soft-feeling, and non-irritating to thewearer's skin. Further, the topsheet is liquid pervious, permittingliquids to readily penetrate through its thickness. A suitable topsheetmay be manufactured from a wide range of materials such as porous foams,reticulated foams, apertured plastic films, natural fibers (e.g., woodor cotton fibers), synthetic fibers (e.g., polyester or polypropylenefibers) or from a combination of natural and synthetic fibers.Preferably, the topsheet is made of a hydrophobic material to isolatethe wearer's skin from liquids in the absorbent core.

A particularly preferred topsheet comprises staple-length fibers havinga denier of about 1.5. As used herein, the term "staple-length fibers"refers to those fibers having a length of at least about 16 mm.

There are a number of manufacturing techniques which may be used tomanufacture the topsheet. For example, the topsheet may be woven,non-woven, spunbonded, carded, or the like. A preferred topsheet iscarded, and thermally bonded by means well known to those skilled in thefabrics art. Preferably, the topsheet has a weight from about 18 toabout 25 g/m², a minimum dried tensile strength of at least about 400g/cm in the machine direction, and a wet tensile strength of at leastabout 55 g/cm in the cross-machine direction.

In a preferred embodiment of the present invention, the top sheetcomprises a PHA of the present invention.

The topsheet and the backsheet are joined together in any suitablemanner. As used herein, the term "joined" encompasses configurationswhereby the topsheet is directly joined to the backsheet by affixing thetopsheet directly to the backsheet, and configurations whereby thetopsheet is indirectly joined to the backsheet by affixing the topsheetto intermediate members which in turn are affixed to the backsheet. In apreferred embodiment, the topsheet and the backsheet are affixeddirectly to each other in the diaper periphery by attachment means suchas an adhesive or any other attachment means known in the art. Forexample, a uniform, continuous layer of adhesive, a patterned layer ofadhesive, or an array of separate lines or spots of adhesive may be usedto affix the topsheet to the backsheet.

In a preferred embodiment of the present invention, the adhesivecomprises a PHA of the present invention.

Tape tab fasteners are typically applied to the back waistband region ofthe diaper to provide a fastening means for holding the diaper on thewearer. The tape tab fasteners can be any of those well known in theart, such as the fastening tape disclosed in U.S. Pat. No. 3,848,594issued to Kenneth B. Buell on Nov. 19, 1974. These tape tab fasteners orother diaper fastening means are typically applied near the corners ofthe diaper.

Preferred diapers have elastic members disposed adjacent the peripheryof the diaper, preferably along each longitudinal edge so that theelastic members tend to draw and hold the diaper against the legs of thewearer. The elastic members are secured to the diaper in an contractiblecondition so that in a normally unrestrained configuration the elasticmembers effectively contract or gather the diaper. The elastic memberscan be secured in an contractible condition in at least two ways. Forexample, the elastic members may be stretched and secured while thediaper is in an uncontracted condition. Alternatively, the diaper may becontracted, for example, by pleating, an elastic member secured andconnected to the diaper while the elastic members are in their relaxedor unstretched condition.

The elastic members may take a multitude of configurations. For example,the width of the elastic members may be varied from about 0.25 mm toabout 25 mm or more; the elastic members may comprise a single strand ofelastic material or the elastic members may be rectangular orcurvilinear. Still further, the elastic members may be affixed to thediaper in any of several ways which are known in the art. For examplethe elastic members may be ultrasonically bonded, heat and pressuresealed into the diaper using a variety of bonding patterns, or theelastic members may simply be glued to the diaper.

In a preferred embodiment of the present invention, the elastic memberscomprise a PHA of the present invention.

The absorbent core of the diaper is positioned between the topsheet andbacksheet. The absorbent core may be manufactured in a wide variety ofsizes and shapes (e.g., rectangular, hour-glass, asymmetrical, etc.) andfrom a wide variety of materials. The total absorbent capacity of theabsorbent core should, however, be compatible with the designed liquidloading for the intended use of the absorbent article or diaper.Further, the size and absorbent capacity of the absorbent core may varyto accommodate wearers ranging from infants through adults.

A preferred embodiment of the diaper has an hour-glass shaped absorbentcore. The absorbent core is preferably an absorbent member comprising aweb or batt of airfelt, wood pulp fibers, and/or a particulate absorbentpolymeric composition disposed therein.

In a preferred embodiment of the present invention, the absorbentpolymeric composition of the absorbent core comprises a PHA of thepresent invention.

Other examples of absorbent articles according to the present inventionare sanitary napkins designed to receive and contain vaginal dischargessuch as menses. Disposable sanitary napkins are designed to be heldadjacent to the human body through the agency of a garment, such as anundergarment or a panty or by a specially designed belt. Examples of thekinds of sanitary napkins to which the present invention is readilyadapted are shown in U.S. Pat. No. 4,687,478, entitled "Shaped SanitaryNapkin With Flaps" which issued to Kees J. Van Tilburg on Aug. 18, 1987,and in U.S. Pat. No. 4,589,876, entitled "Sanitary Napkin" which issuedto Kees J. Van Tilburg on May 20, 1986. It will be apparent that thefilms of the present invention comprising a PHA of the present inventiondescribed herein may be used as the liquid impervious backsheet of suchsanitary napkins. On the other hand it will be understood the presentinvention is not limited to any specific sanitary napkin configurationor structure.

In general, sanitary napkins comprise a liquid impervious backsheet, aliquid pervious topsheet, and an absorbent core placed between thebacksheet and the topsheet. The backsheet comprises a PHA of the presentinvention. The topsheet may comprise any of the topsheet materialsdiscussed with respect to diapers. The adhesives used in may alsocomprise a PHA of the present invention. The absorbent core may compriseany of the absorbent core materials discussed with respect to diapers,including a PHA of the present invention.

Importantly, the absorbent articles according to the present inventionare biodegradable and/or compostable to a greater extent thanconventional absorbent articles which employ materials such as apolyolefin (e.g., a polyethylene) backsheet.

EXAMPLE 1 Poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate)

Poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) is preparedaccording to the general methods described above and based on thepublished procedure of Hori et al. (Hori, Y., M. Suzuki, Y. Takahashi,A. Yomaguchi, and T. Nishishita, MACROMOLECULES, Vol. 26, pp. 5533-5534(1993)) for the polymerization of β-butyrolactone. Specifically,purified [S]-3-methylpropiolactone ([S]-β-butyrolactone) (9.50 g, 110mmol) and [S]-3-isopropylpropiolactone (0.83 g, 5.8 mmol) are chargedinto a septum sealed, argon purged, dry, glass tube via syringe. Theinitiator, 1,3-dichloro-1,1,3,3-tetrabutyldistannoxane preparedaccording to R. Okawara and M. Wada, (J. ORGANOMET. CHEM. (1963), Vol.1, pp. 81-88) and dried overnight in vacuo at 80° C. is dissolved in drytoluene to make a 0.18 M solution. Via syringe, 0.65 mL of the initiatorsolution (0.12 mmol distannoxane) is added to the tube. The tube isgently swirled to mix the contents and then heated at 100° C. for 4 h byimmersing its lower half in an oil bath. As the reaction proceeds, thecontents of the tube become viscous. After the required time, the tubeis removed from the oil bath and allowed to cool to room temperature.The solid is dissolved in chloroform. It is recovered by precipitationinto a hexane-ether mixture, collected by filtration, and dried undervacuum. The comonomer composition of the copolymer is determined by ¹H-NMR spectroscopy and found, within experimental error, to be the sameas the charge ratio (95:5). Molecular weight is determined by sizeexclusion chromatography with chloroform as the mobile phase, and narrowpolystyrene standards are used for calibration.

EXAMPLE 2 Poly(3-hydroxyvalerate-co-3-hydroxy-4-methylvalerate)

Poly(3-hydroxyvalerate-co-3-hydroxy-4-methylvalerate) is prepared byfollowing the same procedure as in Example 1, with the exception that[S]-3-ethylpropiolactone (9.50 g, 94.9 mmol) and[S]-3-isopropylpropiolactone (0.71 g, 5.0 mmol) are used as the monomercharge.

EXAMPLE 3Poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxy4-methylvalerate)

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxy-4-methylvalerate)is prepared by following the same procedure as in Example 1, with theexception that [S]-3-methylpropiolactone (7.20 g, 83.6 mmol),[S]-3-ethylpropiolactone (1.14 g, 11.4 mmol), and[S]-3-isopropylpropiolactone (0.71 g, 5.0 mmol) are used as the monomercharge.

EXAMPLE 4Poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate-co-3-hydroxyoctanoate)

Poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate-co-3-hydroxyoctanoate)is prepared by following the same procedure as in Example 1, with theexception that [S]-3-methylpropiolactone (9.50 g, 110 mmol),[S]-3-isopropylpropiolactone (0.41 g, 2.9 mmol), and[S]-3-pentylpropiolactone (0.50 g, 2.9 mmol) are used as the monomercharge.

EXAMPLE 5Poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxy-4-methylvalerate-co-3-hydroxyoctanoate)

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxy-4-methylvalerate-co-3-hydroxyoctanoate)is prepared by following the same procedure as in Example 1, with theexception that [S]-3-methylpropiolactone (7.20 g, 83.6 mmol),[S]-3-ethylpropiolactone (1.14 g, 11.4 mmol),[S]-3-isopropylpropiolactone (0.36 g, 2.5 mmol), and[S]-3-pentylpropiolactone (0.43 g, 2.5 mmol) are used as the monomercharge.

EXAMPLE 6 Compostable Single Layer Film

Poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) copolymer (PHBMV)of composition 5 mole % methylvalerate/ 95 mole % butyrate is introducedinto a single screw extruder (Rheomix Model 202) with screw diameter of0.75 inch. A constant taper screw having 20:1 length to diameter ratioand a 3:1 compression ratio is employed. The temperature of both heatingzones of the extruder barrel is 25° C. above the melt temperature of thePHBMV. The extruder is equipped with a die of width 6 inch and a die gapof 0.04 inch. The die is maintained at 20° C. above the melt temperatureof the PHBMV. The copolymer is melted within the extruder and pumped tothe die at the other end of the extruder. The screw rpm is kept constantat 30 rpm. The copolymer is forced through the die and is collected on atake-up roll collection system (Postex) at a rate that allowscrystallization of the polymer before take-up. The width of these filmsare nominally 4 inch and the thickness are approximately 0.002 inch.

EXAMPLE 7 Compostable Single Layer Film

Films of PHBMV (95:5) are made by melting the material between Teflonsheets in a Carver Press (Fred S. Carver Inc., Menomonee Falls, Wis.) at20° C. above the melt temperature. Pressure on the sheets are adjustedto produce films of approximately 0.25 mm thick. The films are thenidentically cooled to room temperature by placing the molds betweenlarge (5 kg) aluminum plates and allowing the films to cool to roomtemperature.

EXAMPLE 8 Compostable Multilayer Film

Sheets of PHBMV film may be prepared as in Example 6 of compositionsPHBMV (95:5) and PHBMV (50:50). These sheets may then encase a sheet ofa polymer with good oxygen barrier properties but a poor water vaportransmission rate, or a polymer film that may be water soluble such apoly(vinyl alcohol) (PVA). The films are placed in carver press stackedin the following order PHBMV(95:5), PHBMV(50:50), PVA, PHBMV(50:50),PHBMV(95:5). The material is then pressed at a temperature 5° C. abovethe melt temperature of PHBMV(50:50), but still below the meltingtemperature of the PHBMV(95:5). After compression at 2000 lb for 30 min,the pressure is released and the film is allowed to cool to roomtemperature.

EXAMPLE 9 Compostable Disposable Diaper

A disposable baby diaper according to this invention is prepared asfollows. The dimensions listed are for a diaper intended for use with achild in the 6-10 kilogram size range. These dimensions can be modifiedproportionately for different size children, or for adult incontinencebriefs, according to standard practice.

1. Backsheet: 0.020-0.038 mm film consisting of a 92:8poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) copolymer(prepared as described in Example 1); width at top and bottom 33 cm;notched inwardly on both sides to a width-at-center of 28.5 cm; length50.2 cm.

2. Topsheet: carded and thermally bonded staple-length polypropylenefibers (Hercules type 151 polypropylene); width at top and bottom 33 cm;notched inwardly on both sides to a width-at-center of 28.5 cm; length50.2 cm.

3. Absorbent core: comprises 28.6 g of cellulose wood pulp and 4.9 g ofabsorbent gelling material particles (commercial polyacrylate fromNippon Shokubai); 8.4 mm thick, calendered; width at top and bottom 28.6cm; notched inwardly at both sides to a width-at-center of 10.2 cm;length 44.5 cm.

4. Elastic leg bands: four individual rubber strips (2 per side); width4.77 mm; length 370 mm; thickness 0.178 mm (all the foregoing dimensionsbeing in the relaxed state).

The diaper is prepared in standard fashion by positioning the corematerial covered with the topsheet on the backsheet and gluing.

The elastic bands (designated "inner" and "outer", corresponding to thebands closest to, and farthest from, the core, respectively) arestretched to ca. 50.2 cm and positioned between the topsheet/backsheetalong each longitudinal side (2 bands per side) of the core. The innerbands along each side are positioned ca. 55 mm from the narrowest widthof the core (measured from the inner edge of the elastic bank). Thisprovides a spacing element along each side of the diaper comprising theflexible topsheet/backsheet material between the inner elastic and thecurved edge of the core. The inner bands are glued down along theirlength in the stretched state. The outer bands are positioned ca. 13 mmfrom the inner bands, and are glued down along their length in thestretched state. The topsheet/backsheet assembly is flexible, and theglued-down bands contract to elasticize the sides of the diaper.

EXAMPLE 10 Compostable Lightweight Pantiliner

A lightweight pantiliner suitable for use between menstrual periodscomprises a pad (surface area 117 cm² ; SSK air felt 3.0 g) containing1.0 g of absorbent gelling material particles (commercial polyacrylate;Nippon Shokubai); said pad being interposed between a porous formed-filmtopsheet according to U.S. Pat. No. 4,463,045 and a backsheet whichcomprises a 0.03 mm thickness 92:8poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) copolymercopolymer film, as prepared in accordance with Example 1.

EXAMPLE 11 Compostable Sanitary Napkin

A catamenial product in the form of a sanitary napkin having two flapsextending outward from its absorbent core is prepared using a pad in themanner of Example 10 (surface area 117 cm² ; 8.5 g SSK air felt), perthe design of U.S. Pat. No. 4,687,478, Van Tillburg, Aug. 18, 1987. Thebacksheet and topsheet materials are the same as described in Example10.

EXAMPLE 12 Compostable Sheet

The film preparation procedure of Example 6 is modified by replacing thedie on the extruder with a slot die of thickness approximately 0.25 cmand width 15 cm. Take-up after extrusion is accomplished by insertingthe sheet emerging from the extruder between two counter-rotatingcylinders. The sheet is drawn from the extruder in this manner and cutin lengths of 32 cm. Sheets of approximately 13 cm wide and 0.18 cmthick are obtained.

EXAMPLE 13 Compostable Fiber

PHBMV of composition 5 mole % methylvalerate/95 mole % butyrate isintroduced into a single screw extruder (Rheomix Model 202) with screwdiameter of 0.75 inch. A constant taper screw having 20:1 length todiameter ratio and a 3:1 compression ratio is employed. The temperatureof both heating zones of the extruder barrel is 25° C. above the melttemperature of the PHBMV. The extruder is equipped with a nozzle diecontaining 5 orifices of diameter 500 mm. The die is maintained at 20°C. above the melt temperature of the PHBMV. The polymer is melted withinthe extruder and pumped to the die at the other end of the extruder. Thescrew rpm is kept constant at 30 rpm. The polymer is forced through thedie and the melted extruded fibers are lead through a region where arapid air stream is applied such that the polymer fibers elongates andthins to approximately one fifth of the diameter of the orifices (ca.100 mm). The fibers are collected on a cardboard mat. A widedistribution of fiber lengths are obtained up several cm in length. Mostfiber lengths (over 50%) are in the range of 1.3 to 15 cm.

EXAMPLE 14 Compostable Rigid Foam

PHBMV (40 g) of composition 5 mole % methylvalerate/95 mole % butyrateand 4 g of a common blowing agent, p,p'-oxy-bis benzenesulphonhydrazideare charged to the mixing chamber of a Rheomix type 600 melt blenderequipped with roller blades. The mixing chamber temperature is heatedabove the melting temperature of PHBMV, but below the degradationtemperature of the blowing agent (158° C.). After mixing for 10 minutesat 60 rpm, the copolymer mixture is collected and is transferred to aheated aluminum pan, spread about so that the resulting mass is about0.5 cm in thickness. The copolymer is then place in an oven (NationalAppliance Company, model 5830) and heated to the PHBMV melt temperatureagain, and is held at that temperature until the copolymer is completelymolten (ca. 5 min). The oven temperature is then raised to 160° C. atwhich temperature the blowing agent degrades and copolymer beginsfoaming. At this point the copolymer foam is removed from the oven andis placed into a second oven at a temperature of the maximumcrystallization rate of the PHBMV (about 80° C.). The copolymer is leftin this oven for 6 hours.

EXAMPLE 15 Compostable Flexible Foam

The procedure of Example 14 is used with the following modifications: 40g of poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) copolymer ofcomposition 60 mole % methylvalerate/40 mole % butyrate (PHBMV (40:60))is used in place of PHBMV (95:5).

EXAMPLE 16 Compostable Molded Article

Injection molded articles are obtained by using a Mini Max Molder modelCS-183 (Custom Scientific Instruments, Whippeny, N.J.). The temperatureof the rotor and strator cup is held constant at 20° C. above the melttemperature of the polyhydroxyalkanoate used. About 0.5 grams of PHBMV(95:5) is charged to the stator cup and allowed to melt for 3 minutes.The molten copolymer is radially mixed by raising and lowering the rotortip five times. A dumbbell-shaped steel mold is sprayed with a lightcoating of mold silicone release agent. The mold is placed on the moldsupport wheel of the Mini Max Molder and the molten polymer is injectedinto the mold by action of the rotor tip. The copolymer is molded into adumbbell shaped pieces 0.03 inch thick, 1 inch long, 0.125 inch wide atthe middle of the piece and 0.25 inch wide at the ends. These moldedparts are suitable for mechanical testing.

EXAMPLE 17 Compostable Nonwoven Fabric

Poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) copolymer (PHBMV)of composition 2 mole % methylvalerate/98 mole % butyrate is introducedinto a single screw extruder (Rheomix Model 202, Paramus, N.J.) withscrew diameter of 0.75 inch. A constant taper screw having 20:1 lengthto diameter ratio and a 3:1 compression ratio is employed. Thetemperature of both heating zones of the extruder barrel is 25° C. abovethe melt temperature of the PHBMV. The extruder is equipped with anozzle die containing 5 orifices of diameter 500 mm. The die ismaintained at 20° C. above the melt temperature of the PHBMV. Thepolymer is melted within the extruder and pumped to the die at the otherend of the extruder. The screw rpm is kept constant at 30 rpm. Thepolymer is forced through the die and the melted extruded fibers arelead through a region where a rapid air stream is applied such that thepolymer fibers elongates and thins to approximately one fifth of thediameter of the orifices (ca. 100 mm). The fibers are collected on acardboard mat. The mat is moved in a fashion so that a 10 cm×10 cm areais covered uniformly with fibers. Collection of fibers on the matcontinues, until there is approximately 0.5 cm thick fiber mat. A widedistribution of fiber lengths are obtained up several inches in length.Most fiber lengths (over 50%) are in the range of 0.5 to 6 inches. Themat is then transferred to a Carver Press (Fred S. Carver Inc.,Menomonee Falls, Wis.) and pressed at a 1000 lb force for 10 minutes attemperature 5° C. below the melting temperature of the PHBMV. Theresulting nonwoven sheet is removed from the press.

EXAMPLE 18 Compostable Elastomer

Films of PHBMV (70:30) are made by melting the material between Teflonsheets in a at 20° C. above the melt temperature. Pressure on the sheetsis adjusted to produce films of approximately 0.5 mm thick. The filmsare then identically cooled to room temperature by placing the moldsbetween large (5 kg) aluminum plates and allowing the films to cool toroom temperature. The films are aged for 2 days, then subsequently cutinto strips 10 cm long and 1 cm wide. The strips are then placed in anInstron universal testing machine (Model 1122, Canton, Mass.) and areelongated at a rate of 1 in/min until 300% elongation of the originallength is achieved. The films are held elongated for two days untilcrystallinity develops further. The strips are removed from the Instronand upon subsequent extension, the material returns to its former (postInstron treatment) length.

EXAMPLE 19 Compostable Adhesive

PHBMV (50:50) may be used as a hot-melt adhesive in the followingmanner. About lg of PHBMV (50:50) is placed between two polymer films,such as poly(vinyl alcohol) (PVA), or poly(3-hydroxybutyrate) (PHB) orany other PHA which has a melting temperature at least 10° C. higherthan PHBMV (50:50). The films/adhesive assembly is placed in a CarverPress (Fred S. Carver Inc., Menomonee Falls, Wis.) and is then pressedat a temperature 5° C. above the melt temperature of PHB:MV (50:50).After compression at 2000 lb force for 30 min, the pressure is releasedand the bonded film assembly is allowed to cool to room temperature.

All publications mentioned hereinabove are hereby incorporated in theirentirety by reference.

It is understood that the examples and embodiments described herein arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to one skilled in the art and are tobe included in the spirit and purview of this application and scope ofthe appended claims.

What is claimed is:
 1. A biodegradable copolymer comprising at least tworandomly repeating monomer units wherein the first randomly repeatingmonomer unit has the structure ##STR14## wherein R¹ is H, or C₁ or C₂alkyl, and n is 1 or 2; the second randomly repeating monomer unit hasthe structure ##STR15## and wherein at least 50% of the randomlyrepeating monomer units have the structure of the first randomlyrepeating monomer unit.
 2. The biodegradable copolymer of claim 1,wherein R¹ is a C₁ or C₂ alkyl and n is
 1. 3. The biodegradablecopolymer of claim 2, wherein R¹ is a C₁ alkyl.
 4. The biodegradablecopolymer of claim 1, wherein R¹ is H and n is
 2. 5. A biodegradablecopolymer comprising at least three randomly repeating monomer unitswherein the first randomly repeating monomer unit has the structure##STR16## wherein R¹ is H, or C₁ or C₂ alkyl, and n is 1 or 2; thesecond randomly repeating monomer unit has the structure ##STR17## thethird randomly repeating monomer unit has the structure ##STR18##wherein R³ is H, or a C₁ -C₁₉ alkyl or alkenyl; and m is 1 or 2; whereinat least 50% of the randomly repeating monomer units have the structureof the first randomly repeating monomer unit; and wherein the thirdrandomly repeating monomer unit is not the same as the first randomlyrepeating monomer unit or the second randomly repeating monomer unit. 6.The biodegradable copolymer of claim 5, wherein R¹ is a C₁ or C₂ alkyland n is
 1. 7. The biodegradable copolymer of claim 6, wherein R¹ is aC₁ alkyl.
 8. The biodegradable copolymer of claim 6, wherein m is
 1. 9.The biodegradable copolymer of claim 6, wherein m is
 2. 10. Thebiodegradable copolymer of claim 5, wherein R¹ is H and n is
 2. 11. Thebiodegradable copolymer of claim 10 wherein m is
 1. 12. Thebiodegradable copolymer of claim 10, wherein m is 2.